The present invention relates to a new and distinct blackberry cultivar designated ‘Twilight’ and botanically known as Rubus subg. Rubus Watson. This new blackberry cultivar was discovered in Corvallis, Oreg. in August 2012 and originated from a cross between the thornless female blackberry plant ‘Ouachita’ (U.S. Plant Pat. No. 17,762) and the thornless, male parent blackberry plant ‘ORUS 2867-4’ (unpatented). ‘ORUS 2867-4’ (unpatented) was a selection from a cross of the thornless semi-erect blackberry ‘Triple Crown’ (unpatented) and a thorny trailing blackberry selection ‘ORUS 1393-1’ (unpatented). ‘Twilight's spinelessness was originally derived from ‘Merton Thornless’ (U.S. Plant Pat. No. 571). The original seedling of the new cultivar was asexually propagated at a nursery in Benton County, Oreg. The new cultivar was established in vitro from a cane cutting and microcuttings have been taken and rooted from this sort of culture. The present invention has been found to be stable and reproduce true to type through successive asexual propagations.